The present invention relates to methods and compositions useful in treating existing or placed solids in subterranean formations, and more particularly, to stabilizing relatively unconsolidated portions of subterranean formations, and minimizing the flow back and/or production of unconsolidated particulate material (referred to collectively herein as “particulate migration”).
In the production of hydrocarbons from a subterranean formation, the subterranean formation preferably should be sufficiently conductive to permit desirable fluids, such as oil and gas, to flow to a well bore that penetrates the formation. One type of treatment that may be used to increase the conductivity of a subterranean formation is hydraulic fracturing. Hydraulic fracturing operations generally involve pumping a treatment fluid (e.g., a fracturing fluid or a “pad” fluid) into a well bore that penetrates a subterranean formation at a sufficient hydraulic pressure to create or enhance one or more fractures in the subterranean formation. The fluid used in the treatment may comprise particulates, often referred to as “proppant particulates,” that are deposited in the resultant fractures. These proppant particulates are thought to prevent the fractures from fully closing upon the release of hydraulic pressure, forming conductive channels through which fluids may flow to a well bore.
A type of particulate migration that may negatively affect fluid conductivity in a subterranean formation is the flow back of unconsolidated particulate material (e.g., formation fines, sand, proppant particulates, etc.) through the conductive channels in the subterranean formation, which can, for example, clog the conductive channels and/or damage the interior of the formation or equipment. Production of proppant and formation sand can be problematic because these solids often cause equipment damage, necessitate costly cleanup treatments, and cause potential loss of hydrocarbon production. There are several known techniques used to control particulate migration.
One well-known technique used to control particulate migration in subterranean formations is commonly referred to as “gravel packing,” which involves the placement of a filtration bed of gravel particulates in the subterranean formation, which acts as a barrier to prevent particulates from flowing into the well bore. These gravel packing operations may involve the use of consolidating agents to bind the gravel particulates together in order to form a porous matrix through which formation fluids can pass. In some situations, hydraulic-fracturing operations and gravel-packing operations may be combined into a single operation to stimulate production and to reduce the production of unconsolidated formation particulates. Such treatments are often referred to as “frac-pack” operations. In some cases, these treatments are completed with a gravel-pack screen assembly in place with the fracturing fluid being pumped through the annular space between the casing and screen. In such a situation, the fracturing operation may end in a screen-out condition creating an annular gravel pack between the screen and casing. Another technique that has been used to control particulate migration involves coating proppant particulates with a consolidating agent to facilitate their consolidation within the formation and to prevent their subsequent flow-back through the conductive channels in the subterranean formation. Still another method used to control particulate migration involves consolidating unconsolidated portions of subterranean zones into relatively stable permeable masses by applying a consolidating agent to an unconsolidated portion of the subterranean formation. One example of this method is applying a curable resin to a portion of the zone, followed by a spacer fluid and then a catalyst. Another example of this method involves applying a tackifying composition (aqueous or non-aqueous) to a portion of the formation in an effort to reduce the migration of particulates therein.
Heretofore, many of the well known consolidating agents that have been used in subterranean formations have been introduced to the subterranean formation in a solvent-based carrier fluid like isopropyl alcohol or methanol. Aqueous-based carrier fluids have not typically been used because many known consolidating agents are not soluble or dispersible in water. Problematically, solvent-based carrier fluids usually have a relatively low flash point, which creates safety risks for the transportation of and other operations involving the use of those carrier fluids. Some known consolidating agents comprises a mixture of a furan-based resin derived from furfuryl alcohol. Such mixtures include furfural with the furan-based resin because furfural provides additional polymerization as the resin source, and to help lower the viscosity of the resin mixture. These consolidating agents typically do not comprise an aqueous fluid, because the presence of water on the surface to be consolidated is thought to weaken the bonding between the resin and substrates, preventing the substrates from achieving high cohesion. Accordingly, direct mixing of furan based resin and furfuryl alcohol with water has often been avoided.